1. Field of the Invention
The invention relates to connecting elements provided on pipes and other ducts, for example for the distribution of water or gas.
More precisely, the invention is particularly concerned with proposing a removable sealing-tight flange made in several parts so that it can be mounted on a pipe connecting member, quite particularly within the context of guidance of a relatively flexible tube such as a polyethylene tube used for the interior casing of, in particular, an existing metal piping when it proves faulty, such casing possibly being fitted "under load" (that is to say without interrupting the supply to the user).
2. Description of Related Art
Of course, there are already suitable means of permitting the internal casing of pipes.
At the present time, when for instance localised renovation is required along a cast iron pipe, the current procedure is to dig two pits, upstream and downstream of the faulty portion in order to remove the pipe from the earth at those points. Once the pits are prepared, two branch connections and temporary occlusion systems are put in place, and the pipe is cut at the location of these two pits. Consequently, the part to be cased is defined between the cuts and the gas supply to the users is not interrupted.
In the "upstream" pit (referred to as the entry pit) a monobloc flange fitted with a valve or tap is fitted to the upstream end of the portion to be cased and, by means of an "introducer" (or dolly), the replacement flexible pipe (which of course has a diameter smaller than that of the faulty pipe) is inserted into the cut section. Of course, care will have first been taken to withdraw the temporary occlusion means where necessary.
Once the length of pipe has been cased, a sealing-tight plastic foam is then normally injected around the casing pipe inside the end of the length through which this pipe emerges. The object of the foam is to seal the space between the casing pipe and the cased pipe. Once the foam has set, the operator generally breaks off the end of the portion of pipe situated beyond the block of foam and a fresh foam plug is generally introduced into the end of the metal pipe which is thus prepared, the foam then being normally contained in a bag to form a sealing-tight cone reinforcing the protection provided by the first plug.
As the remaining operations are quite conventional, reference to them will cease at this point. However, it should be noted that the use of such foam plugs does in practice prove to be an operation which is difficult to control, especially for the following reasons;
First of all, the conditions of use depend upon the ambient temperature. In particular, the foam may not be used at temperatures below 5.degree. C.
There are also problems relating to the reliability of the sealing-tightness, taking into account the extent of control of the setting of the products used. For the operations to take place correctly, therefore, it is essential that the personnel should be qualified and well trained.
Furthermore, in spite of the precautions adopted, it is sometimes difficult to control the expansion of the foam inside the pipe, with the inherent risk of the adjacent pipes being occluded.
Moreover, actual operating conditions sometimes result in foaming product being wasted and furthermore, the effective life of the foaming product needs to be monitored.
Finally, it is found that, in the course of time, fluctuations in temperature affect the reliability of the seal, the different nature of the casing pipes (plastics materials) and of the encased pipes (metal, often cast iron or steel) serving only to aggravate this.
To sum up, over and above the question of costs, the existing systems present problems of rational use and viability over the course of time.